<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    const obj = {
      age: ''
    }
    // console.log(obj.age) // ?
    // 如果像用 console.log 看到最用的状态，可以打印对象
    console.log(obj) // ?

    setTimeout(() => {
      obj.age = 19
    }, 1000);
  </script>
</body>

</html>